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gzip, bzip2: add -n flag to suppress modification timestamp

--- a/sys/man/1/gzip

+++ b/sys/man/1/gzip

@@ -3,7 +3,7 @@

 gzip, gunzip, bzip2, bunzip2, compress, uncompress, zip, unzip \- compress and expand data

 .SH SYNOPSIS

 .B gzip

-.RB [ -cvD [ 1-9 ]]

+.RB [ -cvnD [ 1-9 ]]

 .RI [ file

 .BR ... ]

 .PP

@@ -13,7 +13,7 @@

 .BR ... ]

 .PP

 .B bzip2

-.RB [ -cvD [ 1-9 ]]

+.RB [ -cvnD [ 1-9 ]]

 .RI [ file

 .BR ... ]

 .PP

@@ -179,6 +179,19 @@

 Without

 .BR -t ,

 prints the names of files on standard error as they are compressed or decompressed.

+.TP

+.B -n

+The

+.I gzip

+and

+.I bzip2

+file formats include a modification timestamp which is by default set

+to the modification time of the files being compressed or the current

+time when the source file is read from standard input.

+The

+.B -n

+flag overrides this behaviour and puts a timestamp of zero instead,

+making the compressed output deterministic.

 .TP

 .B -D

 Produce debugging output.

--- a/sys/src/cmd/bzip2/bzip2.c

+++ b/sys/src/cmd/bzip2/bzip2.c

@@ -3,7 +3,7 @@

 #include <bio.h>

 #include "bzlib.h"

-static	int	bzipf(char*, int);

+static	int	bzipf(char*, int, int);

 static	int	bzip(char*, long, int, Biobuf*);

 static	Biobuf	bout;

@@ -15,7 +15,7 @@

 static void

 usage(void)

 {

-	fprint(2, "usage: bzip2 [-vcD] [-1-9] [file ...]\n");

+	fprint(2, "usage: bzip2 [-vcnD] [-1-9] [file ...]\n");

 	exits("usage");

 }

@@ -23,9 +23,11 @@

 main(int argc, char **argv)

 {

 	int i, ok, stdout;

+	long mtime;

 	level = 6;

 	stdout = 0;

+	mtime = time(nil);

 	ARGBEGIN{

 	case 'D':

 		debug++;

@@ -36,6 +38,9 @@

 	case 'c':

 		stdout++;

 		break;

+	case 'n':

+		mtime = 0;

+		break;

 	case '1': case '2': case '3': case '4':

 	case '5': case '6': case '7': case '8': case '9':

 		level = ARGC() - '0';

@@ -47,18 +52,18 @@

 	if(argc == 0){

 		Binit(&bout, 1, OWRITE);

-		ok = bzip(nil, time(0), 0, &bout);

+		ok = bzip(nil, mtime, 0, &bout);

 		Bterm(&bout);

 	}else{

 		ok = 1;

 		for(i = 0; i < argc; i++)

-			ok &= bzipf(argv[i], stdout);

+			ok &= bzipf(argv[i], !mtime, stdout);

 	}

 	exits(ok ? nil: "errors");

 }

 static int

-bzipf(char *file, int stdout)

+bzipf(char *file, int nomtime, int stdout)

 {

 	Dir *dir;

 	char ofile[128], *f, *s;

@@ -110,7 +115,7 @@

 		fprint(2, "compressing %s to %s\n", file, ofile);

 	Binit(&bout, ofd, OWRITE);

-	ok = bzip(file, dir->mtime, ifd, &bout);

+	ok = bzip(file, nomtime ? 0 : dir->mtime, ifd, &bout);

 	if(!ok || Bflush(&bout) < 0){

 		fprint(2, "bzip2: error writing %s: %r\n", ofile);

 		if(!stdout)

--- a/sys/src/cmd/gzip/gzip.c

+++ b/sys/src/cmd/gzip/gzip.c

@@ -4,7 +4,7 @@

 #include <flate.h>

 #include "gzip.h"

-static	int	gzipf(char*, int);

+static	int	gzipf(char*, int, int);

 static	int	gzip(char*, long, int, Biobuf*);

 static	int	crcread(void *fd, void *buf, int n);

 static	int	gzwrite(void *bout, void *buf, int n);

@@ -21,7 +21,7 @@

 void

 usage(void)

 {

-	fprint(2, "usage: gzip [-vcD] [-1-9] [file ...]\n");

+	fprint(2, "usage: gzip [-vcnD] [-1-9] [file ...]\n");

 	exits("usage");

 }

@@ -29,9 +29,11 @@

 main(int argc, char *argv[])

 {

 	int i, ok, stdout;

+	long mtime;

 	level = 6;

 	stdout = 0;

+	mtime = time(nil);

 	ARGBEGIN{

 	case 'D':

 		debug++;

@@ -42,6 +44,9 @@

 	case 'c':

 		stdout = 1;

 		break;

+	case 'n':

+		mtime = 0;

+		break;

 	case '1': case '2': case '3': case '4':

 	case '5': case '6': case '7': case '8': case '9':

 		level = ARGC() - '0';

@@ -58,18 +63,18 @@

 	if(argc == 0){

 		Binit(&bout, 1, OWRITE);

-		ok = gzip(nil, time(0), 0, &bout);

+		ok = gzip(nil, mtime, 0, &bout);

 		Bterm(&bout);

 	}else{

 		ok = 1;

 		for(i = 0; i < argc; i++)

-			ok &= gzipf(argv[i], stdout);

+			ok &= gzipf(argv[i], !mtime, stdout);

 	}

 	exits(ok ? nil: "errors");

 }

 static int

-gzipf(char *file, int stdout)

+gzipf(char *file, int nomtime, int stdout)

 {

 	Dir *dir;

 	char ofile[256], *f, *s;

@@ -120,7 +125,7 @@

 		fprint(2, "compressing %s to %s\n", file, ofile);

 	Binit(&bout, ofd, OWRITE);

-	ok = gzip(file, dir->mtime, ifd, &bout);

+	ok = gzip(file, nomtime ? 0 : dir->mtime, ifd, &bout);

 	if(!ok || Bflush(&bout) < 0){

 		fprint(2, "gzip: error writing %s: %r\n", ofile);

 		if(!stdout)